DESCRIPTION: (Applicant's Abstract) This new application concerns the use of behavioral economics to analyze polydrug abuse. Two groups of 5 rhesus monkeys will be used in parallel studies of polydrug abuse. One group of monkeys will have access to methamphetamine and the other group will have access to methadone. The delivery of drugs will be contingent upon the completion of fixed-ratio schedules. Under a fixed-ratio schedule delivery of the reinforcer is contingent upon making a fixed-number of responses. In the present application completion of fixed-ratio schedules will result in the delivery of 0.67 ml of liquid. Depending upon the experimental conditions, the liquid will be water or a solution of drug. Two liquid delivery systems will be present thereby giving the monkey a choice between liquids. In Study 1, either a solution of methamphetamine vs. water, or a solution of methadone vs. water will be present. The concentration of the drug solutions will be varied and also the number of response (i.e. fixed-ratio size) required per liquid delivery will also be systematically changed. The results will be plotted in terms of the drug amount consumed at different prices (i.e combinations of fixed-ratio size and drug concentration). In the next set of studies a series of drug pairs will be analyzed as the price for one drug is changed to different values and the price of the other drug is held constant. In these studies the monkeys will have the option of taking two drugs or just one drug or neither. The focus is on the interactions between intake of drug and their prices. The overall aim is to determine what combinations of drugs are taken when the cost of each drug is varied. The results will demonstrate a systematic and quantitative strategy for the analysis of polydrug abuse.